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Gatzen, Groenemeijer: Forecasting tornadoes using model- and sounding derived parameters
http://physics.uwstout.edu/wx/Notes/
Introduction A: Importance of sounding information doing convective forecasts
Introduction B: Sounding-derived parameters using parcel-theory
Introduction B: Sounding-derived parameters using parcel-theory
CAPE
Introduction B: Sounding-derived parameters using parcel-theory
CAPECIN
Introduction B: Sounding-derived parameters using parcel-theory
CAPECINSBCAPE
Introduction B: Sounding-derived parameters using parcel-theory
CAPECINSBCAPE
Introduction B: Sounding-derived parameters using parcel-theory
CAPECINSBCAPEMUCAPE
Introduction B: Sounding-derived parameters using parcel-theory
CAPECINSBCAPEMUCAPELCL
Introduction B: Sounding-derived parameters using parcel-theory
CAPECINSBCAPEMUCAPELCLLFC
Introduction B: Sounding-derived parameters using parcel-theory
Introduction B: Sounding-derived parameters using parcel-theory
CAPECINSBCAPE
CAPECIN ~ 0 J/kgSBCAPEMUCAPE
Introduction B: Sounding-derived parameters using parcel-theory
CAPECINSBCAPEMUCAPELCL
Introduction B: Sounding-derived parameters using parcel-theory
CAPECINSBCAPEMUCAPELCLLFC
Introduction C: Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
Introduction C: Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
• Horizontal cross sections provide barely enough information for convective forecasts:
Introduction C: Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
• Horizontal cross sections provide barely enough information for convective forecasts: Inversions, moist layers, shear profile not well represented.
Introduction C: Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
• Horizontal cross sections provide barely enough information for convective forecasts: Inversions, moist layers, shear profile not well represented.
• Looking at forecast soundings or vertical cross sections yields required information, but it takes time to find regions of interest.
Introduction C: Sounding-derived parameters in horizontal forecast charts
Is it useful to use them on horizontal maps?
• Horizontal cross sections provide barely enough information for convective forecasts: Inversions, moist layers, shear profile not well represented.
• Looking at forecast soundings or vertical cross sections yields required information, but it takes time to find regions of interest.
• Parameters highlight interesting regions as well as selective variables and are helpful...
• ...to get a brief overview.• ...to compare different numerical models.
Introduction C: Sounding-derived parameters in horizontal forecast charts
Complex parameters using “significant” levels
• Total totals index (TOTL) = T850 + Td850 - 2 * T500 [°C]
• K index = T850 + Td850 - T500 - (T-Td)700 [°C]
• Sweat index = 12*Td850+20*(TOTL-49)+2*U850+5*U500+125*(0.2+sinf) where f=(wind direction500-wind direction850), U=wind speed[kts], TOTL=0 if TOTL<49
Introduction C: Sounding-derived parameters in horizontal forecast charts
Complex parameters using significant levels• Total totals index (TOTL) = T850 + Td850 - 2 * T500 [°C]
• K index = T850 + Td850 - T500 - (T-Td)700 [°C]
• Sweat index = 12*Td850+20*(TOTL-49)+2*U850+5*U500+125*(0.2+sinf) where f=(wind direction500-wind direction850), U=wind speed[kts], TOTL=0 if TOTL<49
We do not use them for tornado forecasting.
• Using them requires a guide of “magical” numbers - and not physical understanding of the weather situation.
“One-slide introduction” of myself…
Pieter Groenemeijer
• (almost) M.Sc. in Meteorology Utrecht University
• Oklahoma University (spring semester 2002)
• 2002 and 2004 European Severe Storms Conferences (Prague, León)
• ESWD (European Severe Weather Database)
• “Sounding-derived parameters associated with large hail and tornadoes in the Netherlands“
• Co-initiator of ESTOFEX (with Johannes Dahl and Christoph Gatzen), Oct, 2002.
Sounding-derived parameters associated with large hail and tornadoes in the NetherlandsPieter Groenemeijer (IMAU; ESTOFEX), Aarnout van Delden (IMAU)
F3 tornado near Deil, 25-06-1967. (A.C. Frenks)
study done at Institute for Marine and Atmospheric Research Utrecht
Sounding-derived parameters associated with large hail and tornadoes in the Netherlands
Main questions
• What sounding-derived parameters can be used to forecast tornadoes?
• ………………….. large hail?
sub-question:
• How do the results differ from studies from the United States?
Basic idea
1. Find soundings taken in the proximity of severe weather events (here: tornadoes)
2. Find if they have special characteristics (w.r.t. other soundings)
method: look at parameters that represent something physical and that have been studied before
Proximity soundings
What is a proximity sounding…?
Used definition:• within 4 hours of the sounding
(before or after)
• within 100 km from a point thatis advected by the 0-3 km meanwind from the sounding locationat the sounding time
• radiosonde observations
Dec 1975 – Aug 2003
(thanks to KNMI, DWD, KMI)
• severe weather reports from Dutch voluntary observers (VWK)
Data sets
Sinds 1974
Vereniging voor Weerkunde en Klimatologie (VWK)
http:/www.vwkweb.nl
Data
soundings associated with: number
hail (2.0 - 2.9 cm)
hail (>= 3.0 cm)
tornadoes F0
tornadoes F1
tornadoes F2
waterspouts
thunder (1990-2000 only)
46
47
24
37
6
26
2045
all soundings 67816
results…
Most-unstable CAPE (MUCAPE)Number of events
maximum
median
75th perc.
25th perc.
MUCAPE not very high with tornadoes…
US studies: MUCAPE highly variable with tornadoes. Strong tornadoes may occur with low CAPE when shear is high
Most-unstable CAPE released below 3 km A.G.L.
MUCAPE<3km high with F0, not with F1+
US studies: Davies (2004) has found a relation between tornado occurrence and high CAPE below 3km (in his study M.L.CAPE)...
(most-unstable) LFC height (m)
LFC relatively low with tornadoes (esp. F0)…
US studies: Davies (2004) has found a relation between low LFC and tornado occurrence
LCL height (50 hPa mixed layer parcel)
US studies: Low LCL favors significant tornadoes, e.g. Craven et al. (2002)
LCL not sign. diff. between tornadic and thunder
LARGE HAIL F0 F1+
Average soundings
note the distribution of parcel buoyancy with height
0-6 km A.G.L. bulk shear (m/s)
0-6 km bulk shear high with F2 tornadoes
US studies: strong tornadoes often occur with supercells associated with >20 m/s 0-6 km shear (e.g. Doswell&Evans, 2003)
0-1 km A.G.L. bulk shear (m/s)
0-1 km shear high with F1, esp. F2 tornadoes..
US studies: strong 0-1 km shear favours for sign. tornadoes (e.g. Craven et al., 2002).
0-1 km A.G.L. storm-relative helicity (m2/s2)
0-1 km shear high with F1, esp. F2 tornadoes..
US studies: high values favor supercell tornadoes (e.g. Rasmussen, 2003).
• F1 and esp. F2 tornadoes occur with higher-than-average 0-1 km shear (and SRH, but less clearly).
• F0 tornadoes (and waterspouts) occur with lower-than-average 0-1 km shear values
• (MU)CAPE is not extreme with tornadoes and thereby has limited value for tornado forecasting..
Some conclusions
• MUCAPE released below 3 km / low LFC heights seem to be important for the formation of weaker (and likely non-supercellular) tornadoes….
(but of course we rather want to forecast the stronger tornadoes)
• LCL heights are probably not as much a limiting factor for tornado development in the NL (and in Germany?) than in much of the U.S.A.
i.e. LCL heights are practically always low enough here for tornadoes
Some conclusions
back to Christoph….
References(ask me if you want to see this slide again)
Craven, J. P., H. E. Brooks, and J. A. Hart, 2002: Baseline climatology of sounding derived parameters associated with deep, moist convection. Preprints, 21st Conference on Severe Local Storms, San Antonio, Texas, American Meteorological Society, 643–646.
Davies, J. M., 2002: On low-level thermodynamic parameters associated with tornadic and nontornadic supercells. Preprints, 21st
Conf. on severe local storms, Kananaskis Park, Alberta, Canada, Amer. Meteor. Soc., 558–592.
Davies, J. M., 2004: Estimations of CIN and LFC Associated with Tornadic and Nontornadic Supercells. Wea. Forecasting, 19, 714–726.
Doswell, C. A. III, and J. S. Evans, 2003: Proximity sounding analysis for derechos and supercells: An assessment of similarities and differences. Atmos. Res., 67-68, 117–133.
Rasmussen, E. N., 2003: Refined supercell and tornado forecast parameters. Wea. Forecasting, 18, 530–535.
Using parameters:A scenario for a weather pattern associated with “critical” values
In collaboration with Lars Lowinski (Meteos Munich) a scenario was designed that is characterized by “critical” values of mentioned parameters.
This scenario is based upon the synoptic situation of four tornado outbreaks over Central Europe:
• Aug. 1st, 1925 (NL, five tornadoes, one F4)• June 1st, 1927 (northwestern GER, four F3/F4 tornadoes)• June 24th, 1967 (northern F, F4/F5 tornadoes)• June 25th, 1967 (NL, four F3/F4 tornadoes)
Using parameters:A scenario for a weather pattern associated with “critical” values
T
H592
584
576
568560
552
500 hPa level
• High geopotential over southern Europe due to well-mixed airmass originating from Atlas mountains
• Strong upper SW-erly jet streak coupled with negatively tilted short-wave trough
Using parameters:A scenario for a weather pattern associated with “critical” values
Surface chart
• Frontal boundary with embedded frontal waves from Iberian Peninsula to northern Germany
• Easterly surface winds over Germany south of Scandinavian surface high pressure system
1015
1020
1015
1010
1010
L
L
H
H
1005
Using parameters:A scenario for a weather pattern associated with “critical” values
3114
2722
1916
moist maritime airmass north of the warm front
rich low-level moisture underneath an inversion north of convergence line
well-mixed airmass south of convergence line
Using parameters:A scenario for a weather pattern associated with “critical” values
3114
2722
1916
Warm sector north of the convergence zone:
• CAPE
• winds veer strongly with height
• strong low-level wind shear
• maybe low LFC heights
• quasigeostrophic forcing due to WAA and DCVA
Using parameters:A scenario for a weather pattern associated with “critical” values
Would this scenario be associated with a tornado outbreak?
1020
1015
1010
1010
L
L
H
H
1005
Using parameters:A scenario for a weather pattern associated with “critical” values
Would this scenario be associated with a tornado outbreak?
We don’t know.
Tornadogenesis is not well understood.
Probably, this scenario is associated with an enhanced chance for tornadoes.
1020
1015
1010
1010
L
L
H
H
1005
Using parameters:23th June, 2004
Christian Schöps
Estofex
23 June, 2004: 500 hPa height, wind speed
23 June, 2004: 850 hPa height, theta-e
23 June, 2004: MUCAPE, deep layer wind shear
23 June, 2004: MUCAPE, low level wind shear
23 June, 2004: LCL height
23 June, 2004: LFC height
Soundings from north-central Germany. Proximity soundings were not available. Soundings indicate...
• rather weak CAPE• winds veer strongly with height• strong low level wind shear• rather low LFC heights
Note: Models did indicate SW-erly surface winds
Conclusions
• Sounding information is essential for convective forecasts.
Conclusions
• Sounding information is essential for convective forecasts.
• Parameters derived from model soundings give a good overview when plotted on maps.
Conclusions
• Sounding information is essential for convective forecasts.
• Parameters derived from model soundings give a good overview when plotted on maps.
• They make it easy to compare different models or model runs.
Conclusions
• Sounding information is essential for convective forecasts.
• Parameters derived from model soundings give a good overview when plotted on maps.
• They make it easy to compare different models or model runs.
• Parameters without physical meaning are not used by Estofex. Learning “magical numbers” associated with complex variables won’t increase our knowledge about tornado forecasting.